1. Field of the Invention
The present invention relates to a method of controlling a hard disk drive and an apparatus therefor, and more particularly, to a method of controlling a track seek servo in a hard disk drive and an apparatus therefor capable of reducing acoustic noise and track seek time.
2. Description of Related Art
A hard disk drive includes magnetic transducers for reading and writing information by sensing magnetic fields of disks and magnetizing the disks, respectively. The information is written in sectors along annular tracks on disk surfaces. There are number of tracks located across each surface of the disk. A group of tracks vertically aligned on the disks are collectively referred to as a cylinder. Accordingly, a track may be identified by a cylinder number.
Each transducer is typically integrated into a slider which is incorporated into a head gimbal assembly (HGA). The HGA is attached to an actuator arm which has a voice coil. The voice coil is located adjacent to a magnetic assembly to define a voice coil motor (VCM). The hard disk drive includes a driving circuit for applying a current to excite the VCM, and a controller. The excited VCM rotates the actuator arm to move the transducer across the disk surface.
When information is read/written, the hard disk drive may perform a seek routine which directs the transducer to move from one cylinder to another cylinder. During the seek routine, the VCM is excited by a current used to move the transducer to a new position on the disk surface. In addition, the controller performs a servo routine that ensures the transducer accurately moves to a cylinder and the center of the track.
It is desirable to minimize the time taken to read/write the information from/to the disks. Therefore, it is also desirable that the seek routine move the transducer to the new cylinder in the shortest possible time. In addition, it is desirable to minimize a settling time for the HGA so that the transducer can speedily read/write information from/to the disk and move to the new cylinder in one time.
Generally, a square waveform acceleration trajectory is employed to control a seek servo in order to speedily move the transducer to a desired track. Unfortunately, since a square wave contains high frequency harmonics which stimulate mechanical resonance in the HGA, the square waveform acceleration excites mechanical components or assemblies with high natural frequencies. This results in acoustic noise, undesirable vibration, and the associated settling time due to residual vibration. The mechanical resonance stimulated by the square waveform acceleration of the related art tends to increase both the settling time and overall time required to read/write the information from/to the disk.
There is proposed a track seek method using a sinusoidal acceleration trajectory in order to solve the aforementioned problems. The associated sinusoidal acceleration, velocity, and position equations are represented as follows.
                                          a            ⁡                          (              t              )                                =                                    K              A                        ⁢                          I              M                        ⁢                          sin              ⁡                              (                                                                            2                      ⁢                                                                                          ⁢                      π                                                              T                      sk                                                        ⁢                  t                                )                                                    ⁢                                  ⁢                              v            ⁡                          (              t              )                                =                                                                      K                  A                                ⁢                                  I                  M                                ⁢                                  T                  sk                                                            2                ⁢                                                                  ⁢                π                                      ⁡                          [                              1                -                                  cos                  ⁡                                      (                                                                                            2                          ⁢                                                                                                          ⁢                          π                                                                          T                          sk                                                                    ⁢                      t                                        )                                                              ]                                      ⁢                                  ⁢                              x            ⁡                          (              t              )                                =                                                                      K                  A                                ⁢                                  I                  M                                ⁢                                  T                  sk                                                            2                ⁢                                                                  ⁢                π                                      ⁡                          [                              t                -                                                                            T                      sk                                                              2                      ⁢                                                                                          ⁢                      π                                                        ⁢                                      sin                    ⁡                                          (                                                                                                    2                            ⁢                                                                                                                  ⁢                            π                                                                                T                            sk                                                                          ⁢                        t                                            )                                                                                  ]                                                          [                  Equation          ⁢                                          ⁢          1                ]            where KA, IM, and Tsk denote an acceleration constant, current amplitude, and track seek time, respectively.
In the track seek method using the sinusoidal acceleration trajectory, the track seek time increases by about 10% in comparison with a track seek method using a square waveform acceleration trajectory. In addition, in the method using the sinusoidal acceleration trajectory, jerks occur at the beginning and end of a track seek, so acoustic noise and vibration are still generated.
As used herein, the term “jerk” refers to a sudden abrupt motion and can be represented by the derivative of acceleration, that is, the rate of change of acceleration. As described above, the jerks occurring at the beginning and end of a track seek cause acoustic noise and vibration.
In the track seek method using the square waveform acceleration trajectory, jerks occurring at the beginning and end of a track seek have infinite values as shown in Equation 2 below.|j(0)|=|j(Tsk)|=∞  [Equation 2]
In the track seek method using the sinusoidal acceleration trajectory, jerks occurring at the beginning and end of a track seek have maximum values as shown in Equation 3 below.
                                          j            ⁡                          (              t              )                                =                                                    K                A                            ⁢                              I                M                                      -                                                            2                  ⁢                                                                          ⁢                  π                                                  T                  sk                                            ⁢                              cos                ⁡                                  (                                                            2                      ⁢                                                                                          ⁢                      π                                                              T                      sk                                                        )                                                                    ⁢                                  ⁢                                                        j              ⁡                              (                0                )                                                          =                                                                  j                ⁡                                  (                                      T                    sk                                    )                                                                    =                                          K                A                            ⁢                              I                M                            ⁢                                                2                  ⁢                                                                          ⁢                  π                                                  T                  sk                                                                                        [                  Equation          ⁢                                          ⁢          3                ]            
Thus, it is to be understood that a seek servo using the sinusoidal acceleration trajectory of Equation 1 experiences fewer jerks than a seek servo using the square waveform acceleration trajectory. However, in the seek servo using the sinusoidal acceleration trajectory, jerks still occur at the beginning and end of a track seek, so acoustic noise and vibration are generated.
In the track seek method using the sinusoidal acceleration trajectory, the sinusoidal acceleration trajectory is previously calculated and its large amount of data is stored in a memory of a microprocessor during a hard disk drive design course, and the data is used to generate the sinusoidal acceleration trajectory during operation of the hard disk drive. Therefore, there is a disadvantage in that a large capacity of the memory is required.
Another technique for reducing acoustic noise in a seek mode is disclosed in Korean Laid Open No. 2001-67380, entitled, “Generalized Fourier Seek Method And Apparatus For A Hard Disk Drive Servomechanism.” According to the technique, seek time and acoustic noise are reduced by using a generalized Fourier seek acceleration trajectory. However, since a generalized Fourier series is represented by a sum of several sinusoidal functions, there is a need to store a table of the several sinusoidal functions in a separate memory. Moreover, since jerks occurring at the beginning and end of a track seek are not considered, the jerks have values of zero at the beginning and end of the track seek, so acoustic noise and vibration still exist.
Generally, an object of a track seek servo in a hard disk drive is to minimize acoustic noise and vibration and move a head to a desired location in the shortest possible time. A so-called “bang-bang” seek controller using a square waveform acceleration trajectory is the most useful one for minimizing seek time but has difficulty in reducing acoustic noise and vibration. A so-called sinusoidal seek controller using a sinusoidal acceleration trajectory has an advantage in reducing acoustic noise and vibration, but it cannot efficiently utilize currents in comparison with the “bang-bang” seek controller. In the sinusoidal seek controller, the seek time increases by about 10%.
Both of the aforementioned conventional seek controllers have jerks at the beginning and end of a track seek, which cause acoustic noise and vibration.
An aspect of the present invention is to design a new acceleration trajectory capable of minimizing the jerks occurring at the beginning and end of a track seek, reducing acoustic noise and vibration, and improving seek performance. Now, the new acceleration trajectory according to the present invention will be described.